Field of the Invention
The present invention relates to a non-reciprocal circuit device and a communication apparatus using the same and, more particularly, to a non-reciprocal circuit device of a distributed constant type and a communication apparatus using the same.
Description of Related Art
A non-reciprocal circuit device such as an isolator or a circulator is incorporated in, for example, a mobile communication apparatus like a mobile phone or a communication apparatus used in a base station. The non-reciprocal circuit devices can be classified into a distribution constant type, a concentrated constant type, and the like. Among them, the non-reciprocal circuit device of the distribution constant type is suitable for use in a base station and the like where high power output signal is required.
A structure of the distribution constant type non-reciprocal circuit device is described in, e.g., Japanese Patent Application Laid-Open No. 1997-121104. The non-reciprocal circuit device described in Japanese Patent Application Laid-Open No. 1997-121104 has a center conductor including three conductors (main conductor portions) extending radially at an angular interval of 120° and three electrode portions (branched conductor portions) extending radially from the roots of the main conductor portions at an angular interval of 120°. This center conductor is placed on a substrate. The substrate is an integrated substrate made up of a ferrite plate in disk shape and a dielectric ring surrounding the ferrite. A leading end of each of the three main conductor portions is connected to an input/output terminal or a terminal resistor, whereby a signal is input/output or terminated. The three branched conductor portions are designed to have such a shape and a size as to obtain intended high-frequency characteristics (e.g., capacitance).
In the non-reciprocal circuit device described in Japanese Patent Application Laid-Open No. 1997-121104, the leading ends of the respective main conductor portions are expanded in a peripheral direction, and the expanded portions cover the dielectric ring. In this case, a large part of the dielectric ring is covered by the center conductor, so that a local stress is less likely to be applied to the dielectric ring during assembly of the non-reciprocal circuit device.
However, when a size of the expanded portion of each of the main conductor portions is reduced in order to obtain intended high-frequency characteristics, the dielectric ring is exposed from the center conductor over a wide range. When the non-reciprocal circuit device is assembled in such a condition, a local stress is applied to some part of the dielectric ring, which may damage the integrated substrate.
In order to prevent the integrated substrate from being damaged, a larger part of the dielectric ring needs to be covered by the center conductor. However, the shape and size of the center conductor are restricted in order to obtain intended high-frequency characteristics, which makes it difficult to adopt such a configuration, depending on the intended high-frequency characteristics.